• S R MISHRA

      Articles written in Pramana – Journal of Physics

    • Dependence of $\it{in-situ}$ Bose condensate size on final frequency of RF-field in evaporative cooling

      S R MISHRA S P RAM S K TIWARI H S RAWAT

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      We report the results of $\it{in-situ}$ characterization of $^{87}$Rb atom cloud in a quadrupole Ioffe configuration (QUIC) magnetic trap after a radio-frequency (RF) evaporative cooling of the trapped atom cloud. The $\it{in-situ}$ absorption images of the atom cloud have shown clear bimodal optical density (OD) profiles which indicate the Bose–Einstein condensation (BEC) phase transition in the trapped gas. Also, we report here, for the first time, the measured variation in the sizes of the condensate and thermal clouds with the final frequency selected in the frequency scan of the RF-field for evaporative cooling. These results on frequency-dependent sizes of the clouds are consistent with the theoretical understanding of the BEC phenomenon in the trap.

    • An analytical approach to the metal and metallic oxide properties of Cu–water and $\rm{TiO_{2}}$–water nanofluids over a moving vertical plate

      B C ROUT S R MISHRA

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      An analysis was carried out to study the flow phenomena of an unsteady, electrically conducting, water-based nanofluid embedded with a porous matrix over a moving/stationary plate. The effects on the nanofluid flow were observed by taking copper (Cu) and titanium oxide ($\rm{TiO_{2}}$) nanoparticles. The crux of the investigation is to examine the influence of thermal radiation, radiation absorption parameter accounted for in the energy equation. The first-order chemical reaction was also taken care of by incorporating it into the solutal transfer equation. Closed form solution holds good for nonlinear coupled partial differential equations. Solutions of these equations are obtained by employing Laplace transform technique. The effects of parameters such as magnetic parameter, porous matrix, thermal and mass buoyancy parameters, thermal radiation, heat absorption parameter, radiation conduction parameter, Prandtl and Schmidt numbers and the homogeneous chemical reaction are shown via graphs. The results for the physical quantities of interest such as the rate of shear stress and the rate of heat and mass transfer coefficients are also obtained and presented through graphs. Observing these, the emerging role of a few parameters is elaborated in the results and discussion section.

    • Simultaneous influence of thermo-diffusion and diffusion-thermo on non-Newtonian hyperbolic tangent magnetised nanofluid with Hall current through a nonlinear stretching surface

      M M BHATTI MAJEED A YOUSIF S R MISHRA A SHAHID

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      In this article, the effect of thermo-diffusion and diffusion-thermo on hyperbolic tangent magnetised nanofluid with Hall current past a nonlinear porous stretching surface has been analysed numerically. The impact of thermal slip and chemical reaction are also examined in our current analysis. Runge–Kutta–Merson method and shooting method have been successfully employed to obtain numerical results for the governing nonlinear differentialequations. The impact of Hartmann number, Hall parameter, porosity parameter, fluid parameter, Weissenberg number, Richardson number, concentration buoyancy parameter, Schmidt number, Dufour parameter, Soret number, Prandtl number, chemical reaction parameter, and power-law exponent are discussed and demonstrated graphicallyfor the flow phenomena. Furthermore, the description for Sherwood number, rate of shear stress, and Nusselt number are displayed using tables against all the pertinent parameters. A detailed numerical comparison for the power-law exponent and Prandtl number has been elaborated via tables.

    • Cooling of fermionic $^{83}\rm{Kr}$ and bosonic $^{84}\rm{Kr}$ isotopes in a magneto-optical trap

      S SINGH V B TIWARI S R MISHRA

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      Simultaneous laser cooling of two isotopes of krypton, $^{83}\rm{Kr}$ and $^{84}\rm{Kr}$, is reported here in a two-isotope magneto-optical trap (TIMOT). The number of cold metastable $^{83}\rm{Kr}$ atoms in this TIMOT is dependent on the power of the repumping laser beams used, which is maximised for our set-up by varying the powers of repumping lasers. These studies may be useful to investigate cold collisions between fermionic $^{83}\rm{Kr}$ and bosonic $^{84}\rm{Kr}$ atoms in the metastable state.

    • Combined effects of free convection and chemical reaction with heat–mass flux conditions: A semianalytical technique

      RAM PRAKASH SHARMA S R MISHRA

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      This paper discusses the effect of heat and mass flux on the natural convective laminar flow of a viscous incompressible fluid under the influence of radiation, magnetic field and Joule heating. The partial differentialequations related to the problem have been changed as a set of ordinary differential equations employing non-dimensional quantities. Semianalytical approach such as the Adomian decomposition method (ADM) is employedto solve the system of ordinary differential equations. The behaviour of characterising parameters on the velocity, heat and mass transfer profiles, and the engineering quantities of interest, i.e. skin friction, heat and mass transfer rates and other indices are presented through graphs

    • Free convective Poiseuille flow through porous medium between two infinite vertical plates in slip flow regime

      PRIYA MATHUR S R MISHRA

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      The present study investigates the heat and mass transfer of magnetohydrodynamic (MHD) free convection through two infinite plates embedded with porous materials. In addition to that the combined effect of viscous dissipation, heat source/sink considered in energy equation and thermodiffusion effect is taken care of in the mass transfer equation. Using suitable non-dimensional variables, the expressions for the velocity, temperature, species concentration fields, as well as shear stress coefficient at the plate, rate of heat and mass transfer, i.e. Nusselt number (Nu) and Sherwood number (Sh) are expressed in the non-dimensional form. These coupled nonlinear differential equations are solved using perturbation technique and their behaviour is demonstrated via graphs for various values of pertinent physical parameters namely, Hartmann number (Ha), Reynolds number (Re), Schmidt number (Sc), Soret number (So), permeability parameter etc. In a particular case, the present result was compared with earlier established results and the results are found to be in good agreement. However, major findings are elaborated in the results and discussion section.

    • Squeezing flow analysis of CuO–water and CuO–kerosene-based nanofluids: a comparative study

      B NAYAK S R MISHRA

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      Heating and cooling are two important procedures in manufacturing as well as transportation industries. Rather than the conventional fluids, solutions of fluids with metal nanoparticles have higher thermal conductivity for effective cooling. Therefore, present paper is a comparative study of squeezing flow analysis of copper oxide–water and oil (kerosene)-based nanofluid between two parallel plates. Magnetohydrodynamic flow of kerosene-based nanofluid along with the dissipative heat energy may enhance the thermal properties of the fluid. Assuming self-similar variables, the governing equations get transformed into non-dimensional forms and approximate analytical techniques such as variation parameter method is employed for these transformed equations. With the well posed physical parameters, the computation is carried out using the mathematical package MATHEMATICA and displayed via graphs and numerical results are shown in tabular form. Favourable cases in comparison with earlier studies are also studied wherever possible. However, when the plates are away from each other, it is seen that the kerosene-based nanofluid velocity overrides the water-based nanofluid whereas the impact is reversed in the case of squeezing.

    • A single laser-operated magneto-optical trap for Rb atomic fountain

      S SINGH B JAIN S P RAM V B TIWARI S R MISHRA

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      A single diode laser and an electro-optic modulator (EOM)-operated magneto-optical trap (MOT) has been developed for a compact atomic fountain. For generating the required cooling and re-pumping laser beams for the MOT, an EOM operating at 6.58 GHz has been used to modulate the input laser beam. In the trapped cold atom cloud, the population in the two ground hyperfine states ($F = 1$ and $F = 2$) of $^{87}$Rb atom has been varied by changing the power applied to EOM. Using this MOT, the cold atoms have been launched vertically upwards and the launch velocity of atoms has been measured. Besides being compact, such MOTs can be useful in atom interferometry set-ups where different atom clouds with different initial hyperfine states need to be prepared.

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